Drupal 8升级至9：Drush篡改数据库命名空间致类找不到错误

问题场景 #

我正在用Composer和Drush完成Drupal 8到Drupal 9的升级，处于数据库更新阶段。执行命令：

vendor/bin/drush updatedb:status

出现错误：

Error: Class 'Drupal\mysql\Driver\Database\mysql\Connection' not found

我的settings.php里数据库命名空间配置为'Drupal\Core\Database\Driver\mysql'，但错误信息里的命名空间被额外插入了一段mysql，变成了Drupal\mysql\Driver\Database\mysql\Connection。即使注释掉settings.php中的命名空间配置，错误依然存在。如果故意把命名空间改成'Drupdddddal\Core\Database\Driver\mysql'，错误就变成：

Class 'Drupdddddal\Core\Database\Driver\mysql\Connection' not found

这说明Drush确实在解析settings.php，但不清楚为什么会篡改命名空间，也不知道如何解决。

原因分析 #

这是Drupal 9数据库驱动结构变化导致的：Drupal 8中MySQL驱动是核心自带的，而Drupal 9将其移到了独立的drupal/mysql模块。如果项目未正确安装该模块，或者升级过程中驱动命名空间的解析逻辑出现过渡问题，就会触发这个错误。

解决步骤 #

1. 安装Drupal 9所需的MySQL驱动模块 #

执行Composer命令安装drupal/mysql：

composer require drupal/mysql

这是Drupal 9及以上版本必须的MySQL数据库驱动，升级后需要单独安装。

2. 修正settings.php中的数据库配置 #

将数据库连接数组里的namespace配置修改为'Drupal\mysql\Driver\Database\mysql'，或者直接删除该配置项——Drupal 9会自动使用正确的默认命名空间。

3. 清除缓存并重新执行命令 #

先清除Drush和Drupal的缓存：

vendor/bin/drush cache:rebuild

再重新运行数据库更新状态命令：

vendor/bin/drush updatedb:status

额外排查点 #

如果以上步骤无效，检查Composer依赖是否正确：

• 执行composer show drupal/core确认Drupal核心版本为9.x；
• 检查composer.json是否存在冲突依赖，比如旧的数据库驱动相关包，执行composer update将所有依赖更新到兼容版本。

完整堆栈信息 #

Error: Class 'Drupal\mysql\Driver\Database\mysql\Connection' not found in /home/XXXXXX/YYYYYYY/vendor/drupal/core/lib/Drupal/Core/Database/Database.php on line 413 #0 /home/XXXXXX/YYYYYYY/vendor/drupal/core/lib/Drupal/Core/Database/Database.php(189): Drupal\Core\Database\Database::openConnection('default', 'default')
#1 /home/XXXXXX/YYYYYYY/vendor/drush/drush/src/Boot/DrupalBoot8.php(194): Drupal\Core\Database\Database::getConnection()
#2 /home/XXXXXX/YYYYYYY/vendor/drush/drush/src/Boot/BootstrapManager.php(352): Drush\Boot\DrupalBoot8->bootstrapDrupalDatabaseValidate(Object(Drush\Boot\BootstrapManager))
#3 /home/XXXXXX/YYYYYYY/vendor/drush/drush/src/Boot/BootstrapManager.php(429): Drush\Boot\BootstrapManager->bootstrapValidate(4)
#4 /home/XXXXXX/YYYYYYY/vendor/drush/drush/src/Boot/BootstrapManager.php(384): Drush\Boot\BootstrapManager->bootstrapToPhaseIndex(5, Object(Consolidation\AnnotatedCommand\AnnotationData))
#5 /home/XXXXXX/YYYYYYY/vendor/drush/drush/src/Boot/BootstrapHook.php(32): Drush\Boot\BootstrapManager->bootstrapToPhase('full', Object(Consolidation\AnnotatedCommand\AnnotationData))
#6 /home/XXXXXX/YYYYYYY/vendor/consolidation/annotated-command/src/Hooks/Dispatchers/InitializeHookDispatcher.php(44): Drush\Boot\BootstrapHook->initialize(Object(Symfony\Component\Console\Input\ArgvInput), Object(Consolidation\AnnotatedCommand\AnnotationData))
#7 /home/XXXXXX/YYYYYYY/vendor/consolidation/annotated-command/src/Hooks/Dispatchers/InitializeHookDispatcher.php(36): Consolidation\AnnotatedCommand\Hooks\Dispatchers\InitializeHookDispatcher->doInitializeHook(Object(Drush\Boot\BootstrapHook), Object(Symfony\Component\Console\Input\ArgvInput), Object(Consolidation\AnnotatedCommand\AnnotationData))
#8 /home/XXXXXX/YYYYYYY/vendor/consolidation/annotated-command/src/Hooks/Dispatchers/InitializeHookDispatcher.php(29): Consolidation\AnnotatedCommand\Hooks\Dispatchers\InitializeHookDispatcher->callInitializeHook(Object(Drush\Boot\BootstrapHook), Object(Symfony\Component\Console\Input\ArgvInput), Object(Consolidation\AnnotatedCommand\AnnotationData))
#9 /home/XXXXXX/YYYYYYY/vendor/consolidation/annotated-command/src/CommandProcessor.php(145): Consolidation\AnnotatedCommand\Hooks\Dispatchers\InitializeHookDispatcher->initialize(Object(Symfony\Component\Console\Input\ArgvInput), Object(Consolidation\AnnotatedCommand\AnnotationData))
#10 /home/XXXXXX/YYYYYYY/vendor/consolidation/annotated-command/src/AnnotatedCommand.php(335): Consolidation\AnnotatedCommand\CommandProcessor->initializeHook(Object(Symfony\Component\Console\Input\ArgvInput), Array, Object(Consolidation\AnnotatedCommand\AnnotationData))
#11 /home/XXXXXX/YYYYYYY/vendor/symfony/console/Command/Command.php(221): Consolidation\AnnotatedCommand\AnnotatedCommand->initialize(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#12 /home/XXXXXX/YYYYYYY/vendor/symfony/console/Application.php(1027): Symfony\Component\Console\Command\Command->run(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#13 /home/XXXXXX/YYYYYYY/vendor/symfony/console/Application.php(273): Symfony\Component\Console\Application->doRunCommand(Object(Consolidation\AnnotatedCommand\AnnotatedCommand), Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#14 /home/XXXXXX/YYYYYYY/vendor/symfony/console/Application.php(149): Symfony\Component\Console\Application->doRun(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#15 /home/XXXXXX/YYYYYYY/vendor/drush/drush/src/Runtime/Runtime.php(124): Symfony\Component\Console\Application->run(Object(Symfony\Component\Console\Input\ArgvInput), Object(Symfony\Component\Console\Output\ConsoleOutput))
#16 /home/XXXXXX/YYYYYYY/vendor/drush/drush/src/Runtime/Runtime.php(51): Drush\Runtime\Runtime->doRun(Array, Object(Symfony\Component\Console\Output\ConsoleOutput))
#17 /home/XXXXXX/YYYYYYY/vendor/drush/drush/drush.php(72): Drush\Runtime\Runtime->run(Array)
#18 /home/XXXXXX/YYYYYYY/vendor/drush/drush/drush(3): require('/home/XXXXXX/...')
#19 /home/XXXXXX/YYYYYYY/vendor/bin/drush(115): include('/home/XXXXXX/...')
#20 {main}

内容的提问来源于stack exchange，提问作者Paul P